Powder-dusting apparatus

ABSTRACT

A powder-dusting apparatus (4) which inside a printing machine dusts the pre-dried printed products coming from the printing unit with a powder, for example of corn-starch, comprises in a manner known per se a plurality of nozzles (6), which are charged with a mixture of powder and carrying air from a mixing device (8). The nozzles (6) are arranged in the vicinity of the plane of transport defined by the transport system (1) of the printing machine and are able to assume two different spacings with respect to that plane: ordinarily the nozzles (6) are located comparatively close to this plane of transport; during these times the mixture of powder and carrying air emerges from the nozzles (6) towards the printed products moving past. If, however, a gripping device (2), which is part of the transport system (1) and which holds the printed product, enters the vicinity of the nozzles (6), a suitable control means (9 to 12) causes the nozzles to move into a second position. In this position there is between the underside of the nozzles (6) and the plane of transport of the transport system (1) sufficient space for the gripping device (2) to be able to pass.

This is a 371 of PCT/EP96/04635, filed on Oct. 25, 1996.

The invention relates to a powder dusting apparatus for a printingmachine, having

a) a plurality of nozzles through which a mixture of powder and carryingair is directed towards the printed products moved past by grippingdevices of the transport system of the printing machine;

b) a mixing device, in which the powder is mixed with air to produce themixture of powder and carrying air;

c) at least one connecting line, which connects the mixing device withthe nozzles.

Powder-dusting apparatuses of that kind serve to provide printingmachine products which are coming from the print unit and which havepassed through a drying zone with a coating of powder, which preventsthe printed products from sticking together during the stackingoperation that follows. For that purpose the powder-dusting apparatusesare arranged in the vicinity of the plane of transport of the printedproducts so that their nozzles are able to apply a mixture of air(carrying air) and powder to the printed products. Generally speaking,the transport systems of printing machines are formed by parallelendless conveyor chains which are joined to one another by a pluralityof gripping devices. The gripping devices comprise a gripping mechanism,which is able to hold the printed products at their edge, and projectbeyond the plane of transport of the printed products. In knownpowder-dusting apparatuses, the nozzles therefore have to be acomparatively large distance from the plane of transport so that thegripping devices are able to get past. This large distance has thedisadvantage, however, that the mixture of powder and carrying air thatis expelled from the nozzles spreads out uncontrollably in the printingmachine.

It is the aim of the present invention to construct a powder-dustingapparatus of the kind mentioned in the introduction in such a mannerthat the mixture of powder and carrying air can be applied in aspatially concentrated manner to the printed products.

That problem is solved according to the invention by

d) a lifting device which is able to move the nozzles back and forthbetween two positions, namely,

da) a first position comparatively far removed from the plane oftransport of the printed products

and

db) a second position lying comparatively close to the plane oftransport of the printed products,

and

e) a control means detecting the position of the gripping devices, whichcontrol means co-operates with the lifting device such that the latterbrings the nozzles into the first position as long as gripping device isin the vicinity of the nozzles, and brings the nozzles into the secondposition when the gripping device is located an adequate distance fromthe nozzles.

According to the invention, the nozzles of the powder-dusting apparatusare therefore no longer fixedly mounted. On the contrary, they are givena mobility perpendicular to the plane of transport of the printedproducts so that they are able to "make way" for gripping devicesapproaching them, that is, maintain a correspondingly large distancefrom the plane of transport in the comparatively short period in whichthe gripping devices travel past beneath the nozzles. As soon as thegripping device has passed the nozzles, however, these return to aposition in which they are very close to the plane of transport and thusto the surfaces of the printed products to be dusted. The proximity ofthe nozzle openings to the printed products allows a more controlleddusting than was previously possible with known powder-dustingapparatuses.

The lifting device and the control means alike can be realised in manydifferent ways. In a first exemplary embodiment of the invention, bothlifting device and control means are mechanically constructed andcombined with one another. They are distinguished in that the liftingdevice and the control means are combined in a cam mechanism whichcomprises:

a) at least one chain wheel co-operating with a conveyor chain of thetransport system;

b) at least one inherently closed cam surface carried by the chainwheel;

c) at least one cam follower connected to the nozzles, which co-operateswith the cam surface;

d) a guide means, which guides the nozzle on the path between its twopositions.

In this practical form, the relative position of the gripping devices onthe transport system and the nozzles is mechanically detected; thelifting mechanism requires no special driving means and the controlmeans requires no power supply of its own. This exemplary embodiment isespecially robust and not susceptible to faults.

It is preferred therein that two parallel cam surfaces are provided,which form a cam track in which the cam follower is received. The twoparallel cam surfaces guide the cam follower in both possible directionsof movement, so that the latter is able to fulfil its function withoutthe assistance of further components.

Alternatively, however, a form in which only one cam surface is providedand the cam follower is pressed by a biassing device against the one camsurface is perfectly possible and structurally somewhat more simple. Inthis practical form of the invention movement of the nozzles in onedirection is therefore effected under the influence of the cam surface,which presses the nozzles back against the action of the biassingdevice, whilst movement in the other direction is effected by thebiassing device, which holds the cam follower of the nozzles in contactwith the (backwardly moving) cam surface.

In principle it is possible, however, and in many cases also easier, forthe lifting device to be separated mechanically from the control means.The latter can then also be of electrical/electronic constructionwithout problems. For that purpose it can comprise a first sensor whichis arranged at the plane of transport and which, as a gripping deviceapproaches the nozzles, gives to the lifting device a first signal whichcauses the lifting device to bring the nozzle into the first position.The sensor can be any device which responds to the physical proximity ofthe gripping device, for example, all forms of proximity switches, lightbarriers, alternatively also mechanical switches of which the operatingelement is operable by the gripping devices as these move past. The"restoration" of the nozzles into the (second) position close to theplane of transport can here in turn be effected by different methods:

It is thus possible, for example, for the control means to comprise asecond sensor which is arranged at the plane of transport and which, asa gripping device moves away, gives a second signal to the liftingdevice which causes the lifting device to bring the nozzle into thesecond position.

Alternatively, a form of the invention is possible in which the controlmeans contains a timing element which is triggered by the first signalof the first sensor and after a certain period has elapsed emits asecond signal which is supplied to the lifting device and causes this tobring the nozzles into the second position. This variant is likely onthe whole to be less expensive than the above-mentioned control meansoperating with two sensors. The period defined by the timing elementbetween the appearance of the first and the second signal is selected sothat it is sufficient to allow the gripping device to pass by thenozzles at the particular speed of the transport system.

Depending on the structural circumstances of the individual case, one ofthe two following variants, namely, the combination of the nozzles toform a nozzle assembly, can prove especially favourable.

The first variant is distinguished in that the nozzles are rigidlyconnected to a distributer pipe and with this form a movable unit whichis connected by way of a flexible hose to the mixing duct. This variantmanages with a single flexible hose, which is advantageous in respect ofuse of material and in respect of installation costs. Nevertheless adistributer pipe rigidly connected to the nozzle generally also means asomewhat larger moving mass.

If the size of the moving mass is of prime importance, then a practicalform of the invention can be selected in which the nozzles are connectedby means of a light-weight supporting bar to form a movable unit andeach nozzle is connected by way of a flexible hose to a fixeddistributer pipe, which in its turn is in connection with the mixingdevice. In this embodiment the distributer pipe is therefore not movedwith the nozzles; the cohesion of the nozzle assembly which combines thedifferent nozzles to form a whole, is effected by means of thesupporting bar, which can be very much lighter in weight than adistributer pipe. In this case, however, a connection has to be madebetween each nozzle and the distributer pipe by way of a flexible hose.

Especially preferred is an embodiment of the invention which comprises asensor which detects the position of the nozzles and produces an outputsignal that causes the mixing device to function only for as long as thenozzles are located in the second position (close to the plane oftransport). Dusting is therefore interrupted for as long as the nozzlesare lifted into the first position for passage of a gripping device;this enables the abovementioned disadvantages, which are found in knownpowder-dusting apparatuses, to be avoided also in these intervals.

The lifting device can be especially simply controlled when it displacesthe nozzles in a pivoting movement between the two positions.

This can be realised in structural terms in that the lifting devicecomprises a one-armed or multi-armed lever which at a first pointcarries the nozzles and at a second point is driven by a cam surface.

The cam surface serving to move the nozzles between the two positions isadvantageously constructed and driven so that one revolution of the camsurface corresponds to the advancement of the transport system of theprinting machine by the spacing of two successive gripping devices.

This synchronisation of the cam surface movement with the movement ofthe printed products can be realised especially easily in that thecircumference of a chain wheel driving the cam surface is selected to bethe same as the spacing of successive gripping devices of the transportsystem.

Exemplary embodiments of the invention are explained in greater detailhereinafter with reference to the drawings, in which:

FIG. 1 shows diagrammatically the delivery region of a printing machine;

FIG. 2 shows, likewise diagrammatically, a powder-dusting apparatusprovided in the printing machine of FIG. 1 in a first position of thenozzles;

FIG. 3 is a view corresponding to FIG. 2, but in which the nozzles arelocated in a second position;

FIG. 4 is a view of a chain wheel bearing a cam track which is used inthe powder-dusting apparatus of FIGS. 2 and 3; and

FIGS. 5 to 7 are diagrammatic representation of a further modifieddrive.

FIG. 1 illustrates the delivery region of a printing machine. The actualprinting unit is imagined to be to the right of the illustrated region.The printed products are moved through the entire printing machine bymeans of a conveyor system, which comprises two endless conveyorchains 1. The conveyor chain 1 visible in FIG. 1 lies behind the planeof projection; a corresponding endless conveyor chain 1, runningparallel to the illustrated conveyor chain 1, is mounted in front of theplane of projection of FIG. 1. The two conveyors chains 1 are connectedto one another by a plurality of gripping devices 2, which extendperpendicular to the plane of projection of FIG. 1 and on each of whicha gripping mechanism for gripping a printed product is mounted. Theconstruction of such gripping devices 2 is known per se.

The gripping devices 2 are arranged at regular intervals apart along theconveyor chains 1 and transport the printed products from the intakeregion of the printing machine, not illustrated, through the printingunit, also not illustrated, and then in the direction of arrow 3 past apowder-dusting apparatus 4, indicated merely diagrammatically in FIG. 1,to a pile 5, on which they are deposited.

Between the printing unit and the powder-dusting apparatus 4, there isgenerally a drying zone, in which the printed products, still damp fromprinting, are substantially dried off, for example, in the region of theconveyor path denoted by the reference number 6'. Since the printedproducts in the drying zone, the length of which has to be kept withinlimits for reasons of economy, are not dried so completely that mutualadhesion is excluded, the powder-dusting apparatus 4 is provided, withwhich a coating of powder is applied to the printed products. Thisprevents the superimposed printed products from sticking to one anotherin the pile 5.

An exemplary embodiment of such a powder-dusting apparatus 4 isillustrated in FIGS. 2 and 3 on an enlarged scale. A plurality ofnozzles 6, which are fed by way of a common distributer pipe 7, isinstalled at the plane of transport of the printed products moved pastby means of the conveyor chains 1. The distributer pipe 7 is connectedby way of a flexible hose 16 to a mixing device 8 in which the powder,generally a corn-starch product, is mixed with carrying air and is thusconveyed to the nozzles 6.

A chain wheel 9 is rotatably mounted by means of an axle stub 10 in themachine housing, which is not illustrated specifically, and engages withthe transport chain 1, which in FIGS. 2 and 3 is moved behind the planeof projection in the direction of arrow 3.

The circumference of the chain wheel 9 corresponds to the spacing atwhich the gripping devices 2 are carried by the conveyor chains 1.

As is especially apparent from FIG. 4, in the chain wheel 9 on the sidefacing towards the distributer pipe 7 there is formed a cam track 11which comprises cam surfaces 11a, 11b running parallel to one another.The form of the cam track 11 is as follows:

For a comparatively small angle α the cam track 11 follows an arc of acircle which is concentric with the centre of rotation of the chainwheel 9 and has a comparatively small radius. Adjoining the angle regionα on each side over angles β₁, and β₂ are transition regions in whichthe cam track 11 changes from the smaller radius to a larger radius. Forthe remaining angle region the cam track 11 follows an arc of a circlewhich is likewise concentric with the centre of rotation of the chainwheel 9, but has a larger radius.

The distributer pipe 7 is provided with a pin 12 projecting in the axialdirection and serving as cam follower, which engages in the cam track11. The distributer pipe 7, and thus the nozzles 6, are displaceable ina vertical direction between two guides 13, which are indicated in thedrawing by broken lines. The arrangement is therefore such that thevertical position of the nozzles 6 is determined by the cam track 11,ultimately therefore by the rotated position of the chain wheel 9.

The spacing of two successive gripping devices 2 on the transport chain1 corresponds to the circumference of the chain wheel 9, respectively toan integral multiple thereof. The chain wheel 9 is mounted so that thecam track 11 in the angle region α, in which it follows the arc of thecircle of relatively small diameter, is located in engagement with thecam follower 12 of the distributer pipe 7 as a gripping device 2 ispassing beneath the nozzles 6.

The powder-dusting apparatus 4 described above operates as follows:

As long as there is no gripping device 2 in the vicinity of the nozzles6, as illustrated in FIG. 3, the cam follower 12 on the distributer pipe7 is located in the region of the cam track 11 of larger radius. Thismeans that the distributer pipe 7 with the nozzles 6 attached thereto islowered comparatively far down between the guides 13. The openings ofthe nozzles 6 are located comparatively close to and opposite theprinted products being moved past in the plane of transport defined bythe conveyor chains 1. That means that the mixture of powder andcarrying air which emerges from the nozzles 6 has only comparativelylittle opportunity to escape laterally.

Shortly before the next gripping device 2 approaches the nozzles 6, thetransition region of the cam track 11b, which corresponds to the angleβ¹ (FIG. 4) and which leads in the direction of rotation (arrow 14) ofthe chain wheel 9, comes into engagement with the cam follower 12 sothat the distributer pipe 7 together with the nozzles 6 is raised duringthe rotation of the chain wheel 9 through the angle β₁. Distributer pipe7 and nozzles 6 remain in this raised position, which is illustrated inFIG. 2, for the period in which the chain wheel 9 passes through theangle α. Within this period the gripping device 2 moves on beneath thenozzles 6 for which there is sufficient space by virtue of thecomparatively large distance between the nozzles 6 and the plane oftransport defined by the conveyor chains 1. Once the gripping device 2has passed through, the cam follower 12 of the distributer pipe 7 entersthe transition region of the cam track 11 in the chain wheel 9 which isassociated with the lagging angular region β₂. In that region the camfollower 12, and thus the distributer pipe 7 and the nozzles 6 attachedthereto, is transferred again into the region of the cam track 11 whichhas the larger radius. This transfer of the cam follower 12 isaccompanied by lowering of the distributer pipe 7, displaceable betweenthe guides 13, and of the nozzles 6 into the position illustrated inFIG. 3.

As a result, the conditions are such that the nozzles 6 pull backbriefly from the transport plane of the printed products in order toallow a gripping device 2 to pass, and immediately thereafter return toa position adjacent to the plane of transport again.

In FIGS. 2 and 3, at the level which the distributer pipe 7 and thenozzles 6 assume in the lowered position, above the plane of transportof the printed products, a sensor 15 is provided, which detects thepresence of the lowered distributer pipe 7 and the lowered nozzles 6. Inthe case of the exemplary embodiment of the sensor 15 illustrated in thedrawing, the sensor is a reflected light barrier. Equally well suited,however, are all types of proximity switches or a mechanicalmicro-switch, the operating element of which lies in the path ofmovement of the nozzles 6 or of a component moving together with these.

If the nozzles 6 and the distributer pipe 7 are lowered, the sensor 15supplies a starting signal to the mixing device 8. The mixing device 6then conveys the mixture of powder and carrying air though the flexiblehose 16 to the distributer pipe 7 from which is emerges by way of thenozzles 6 towards the printed products. If, however, the sensor detectsthat, as illustrated in FIG. 2, the nozzles 6 and the distributer pipe 7have been raised for passage of a gripping device 2, it supplies aswitch-off signal to the mixing device 8, so that no powder is blown outof the nozzles 6 during that time.

In the exemplary embodiment illustrated in FIGS. 2 to 4, the camarrangement which effects raising and lowering of the nozzles 6 is inthe form of a cam track 11 with two oppositely disposed cam surfaces 11aand 11b. The cam follower 12 is therefore positively guided between thetwo cam surfaces 11a and 11b both in an upward direction and in adownward direction. In the case of the embodiment shown in FIG. 6, onthe other hand, only the (inner) cam surface 11a arranged closer to themidpoint of the chain wheel 9 is provided. The nozzles 6 and thedistributer pipe 7 are urged upwards by a biassing device, for example,a spring 22, so that the cam follower 12 remains constantly inengagement with that one cam surface 11a even without guidance from acounter-element.

In a further embodiment of the powder-dusting apparatus 4 shown in FIG.7, control of the lifting and lowering movement is effectedelectronically. To that end the distributer pipe 7 with the nozzles 6 issecured to a pneumatic cylinder 23 or a different lifting drive (forexample, a magnetic drive) which is capable of moving distributer pipe 7and nozzle 6 vertically up and down between two positions. The approachof a gripping device 2 towards the nozzles 6 is detected by a firstsensor 24, for example, a (reflected) light barrier. This first sensor24 then supplies a first signal to the lifting device 23 which thereuponmoves the nozzles 6 and the distributer pipe 7 into the upper position.When the gripping device 2 has moved past the nozzles 6, it passesthrough a second sensor 25 which can be of similar construction to thefirst sensor 24. As the gripping device 2 passes, this second sensor 25supplies a second signal to the lifting device 23, whereupon the latterreturns the nozzles 6 and the distributer pipe 7 into the positionadjacent to the transport plane of the printed products again. In thisembodiment, the sensors 24,25 which act on the lifting device can alsobe used to switch the mixing device 8 on and off. Instead of twosensors, 24,25 one of which is arranged upstream of the nozzles and theother of which is arranged downstream of the nozzles 6 (viewed in thedirection of transport), it is also possible to use just a single sensor24 positioned upstream of the nozzles as shown in FIG. 8. The firstsignal that this sensor 24 produces as a gripping device 2 moves past issupplied not only to the lifting device 23 (which moves the nozzles 6and 7 upwards), but also to a timing element 26. After elapse of aspecific time within which the gripping device 2 has moved past thenozzles 6, the timing element produces a second signal which commandsthe lifting device 23 to lower the nozzles 6 and the distributer pipe 7downwards again. It is also possible in that case to utilise the sensorsignal and the output signal of the timing element 26 to control themixing device 8 in order in this manner to ensure that the mixture ofpowder and carrying air emerges from the nozzles 6 only when these arein the lowered position.

In the case of the exemplary embodiment of the powder-dusting apparatusdescribed with reference to FIGS. 2 to 4, a complete nozzle assembly,consisting of distributer pipe 7 and the nozzles 6, is moved verticallyup and down. In this case a single flexible hose 16 which provides theconnection between the mixing device 8 and the distributer pipe 7 issufficient. Under some circumstances, in order to reduce the movingmasses, it can be advantageous to secure the distributer pipe 7 fixedlyto the machine frame and to move only the nozzles vertically up anddown, which in this case are held together by a very light-weightconnecting bar. In this embodiment of the invention a flexible hoseleads from each nozzle to the distributer pipe.

In the exemplary embodiment mentioned above, the movement of the nozzlesbetween the two positions which they are able to assume relative to theplane of transport was linear. The control of the movement sequence in afurther exemplary embodiment of the invention, which is illustrated inFIG. 5, is effected even more simply:

Here, the lifting device comprises a double-arm lever 17, on one arm 18of which the nozzles 6 are arranged and the other arm 19 of which isdriven by a cam surface 11a, 11b, for which purpose the arm engages witha drive pin 20 in the cam track 11. The lever 17 is mounted on a pin 21secured to the machine frame. The chain wheel 9 turns the cam track 11synchronously with the movement of the conveyor chains 1, and thenozzles consequently have imparted to them a pivoting movement from oneposition into the other position. As in the exemplary embodiments shownin FIGS. 2 to 5, the cam track 11 is mounted on the chain wheel 9, thecircumference of which corresponds to the spacing of two successivegripping devices 2. The phase position of the chain wheel 9 is matchedduring installation to the phase position of the gripping devices 2, sothat as a gripping device 2 passes by, it is possible to ensure thateach nozzle 6 is lifted an adequate distance away from the pathtravelled by the printed products.

I claim:
 1. Powder-dusting apparatus for a printing machine, having atransport system including gripping devices,a) a plurality of nozzlesthrough which a mixture of powder and carrying air is directed towardsprinted products moved past by the gripping devices of the transportsystem of the printing machine; b)a mixing device, in which the powderis mixed with air to produce the mixture of powder and carrying air; c)at least one connecting line, which connects the mixing device with thenozzles, characterized by d) a lifting device (9 to 13) which is able tomove the nozzles (6) back and forth between two positions, namely,da) afirst position comparatively far removed from a plane of transport ofthe printed products and db) a second position lying comparatively closeto the plane of transport of the printed products and e)a control means(11, 12) detecting the position of the gripping device (2), whichcontrol means co-operates with the lifting device (9 to 13) such thatthe latter brings the nozzles (6) into the first position as long as thegripping device (2) is in the Vicinity of the nozzles (6), and bringsthe nozzles (6) into the second position when the gripping device (2) islocated an adequate distance from the nozzles (6).
 2. Powder-dustingapparatus according to claim 1, characterised in that the lifting deviceand the control means are combined in a cam mechanism (9 to 13) whichcomprises:a) at least one chain wheel (9) co-operating with a conveyorchain (1) of the transport system; b) at least one inherently closed camsurface (11a, 11b) driven by the chain wheel (9); c) at least one camfollower (12) connected to the nozzles (6), which co-operates with thecam surface (11a, 11b); d) a guide means (13), which guides the nozzles(6) on the path between their two positions.
 3. Powder-dusting apparatusaccording to claim 2, characterised in that two parallel cam surfaces(11a, 11b) are provided, which form a cam track (11) in which the camfollower (12) is received.
 4. Powder-dusting apparatus according toclaim 2, characterised in that only one cam surface is provided and thecam follower is pressed by a biassing device against the one camsurface.
 5. Powder-dusting apparatus according to claim 1, characterisedin that the lifting device is mechanically separated from the controlmeans and the latter comprises at least a first sensor arranged at theplane of transport which, as a gripping device approaches the nozzles,supplies to the lifting device a first signal which causes the liftingdevice to bring the nozzle into the first position.
 6. Powder-dustingapparatus according to claim 5, characterised in that the control meanscomprises a second sensor arranged at the plane of transport which, as agripping device moves away, supplies a second signal to the liftingdevice which causes the lifting device to bring the nozzles into thesecond position.
 7. Powder-dusting apparatus according to claim 5,characterised in that the control means contains a timing element whichis triggered by the first signal of the first sensor and after a certainperiod has elapsed emits a second signal which is supplied to thelifting device and causes this to bring the nozzles into the secondposition.
 8. Powder-dusting apparatus according to claim 1,characterised in that the nozzles (6) are rigidly connected to adistributer pipe (7) and with this form a movable unit which isconnected by way of a flexible hose (16) to the mixing device (8). 9.Powder-dusting apparatus according to claim 1, characterised in that thenozzles are connected by means of a light-weight supporting bar to forma movable unit and each nozzle is connected by way of a flexible hose toa fixed distributer pipe, which in its turn is in connection with themixing device.
 10. Powder-dusting apparatus according to claim 1,characterised in that it comprises a sensor (15) which detects theposition of the nozzles (6) and produces an output signal that causesthe mixing device (8) to function only for as long as the nozzles (6)are located in the second position.
 11. Powder-dusting apparatusaccording to claim 1, characterised in that the lifting device displacesthe nozzles in a pivoting movement between the two positions. 12.Powder-dusting apparatus according to claim 11, characterised in thatthe lifting device comprises a one-armed or multi-armed lever which at afirst point carries the nozzles (6) and which at a second point isengaged by a cam surface (11) driven synchronously with the speed atwhich the printed products are conveyed.
 13. Powder-dusting apparatusaccording to claim 2, characterised in that the cam surface (11a, 11b)performs one revolution for advancement of the conveyor chain (1) by adistance that corresponds to the spacing of two successive grippingdevices (2).
 14. Powder-dusting apparatus according to claim 13,characterised in that the circumference of the chain wheel (9)corresponds to the spacing of successive